| LECTURE-1 : LECTURE-1 UNITS AND DIMENSION ::
Why do we need units ?
We need units because we want to measure the
Amount or quantity of some things. To make this
measurement globally acceptable we need to put some
Unique measurement value. This value is called a UNIT
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| Slide2 :
Dimensions are physical quantities like length, mass, time which
Uniquely characterises an object.
If say you want to measure the distance then its dimension is the
Length. For matter its mass and for clock it’s the time
Units are used to measure this physical quantities.
Meter for example is the metric unit for length
Units are of two types----
1. Metric system (European and other countries)
2. Foot-Poundal system (USA) What are dimensions ? |
| Slide3 : If you are measuring a very big quantity then you represent your
Measure with a bigger unit.
For example take length of a stick and the distance between OK
city and Stillwater. The first one you can measure with a unit as
Small as meter, What about the second one ?
If we want to measure the distance in meters(m) or foot(ft) it is
fine but it
Is going to be a very big number. Rather it will be easy to
represent the distance in tems of a bigger Unit called
KILOMETER(Km) or in MILES (miles)
Units can be small and big… |
| How big or small can a Unit be ?? : How big or small can a Unit be ?? A unit can be as big as 26,000 Light years, where
1 Lightyear = Distance travelled by Light in 1 year
= 3x108 x60x60x24x365 m
= 3.942x1014 m
It’s a large distance !!!!
26,000 Light year is the distance between Sun and the
center of our Galaxy the MILKY WAY.
So we see that Light year is a very big unit as compared
to meter though they both represent length
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| Slide5 : Let us now see how small a unit can be,
If we ask the question as to what is the radius of an
Atom, the smallest unit of matter ?
The answer is a few angstrom ~ 10-8 m
Or that is ~ 0.00000001 m
Hence we see that the span of measurable quantity
having same dimension for example length can be very
Wide. So we require convenient units while measuring
big or small quantities |
| Slide6 : 1 Km = 1000 m
1m = 100 cm (centimeter)
1mile = 5280 ft
1ft = 12 inch
1inch =2.54 cm
The relation between the unit of length in metric
System.And the foot-poundal system is ::
1 ft = (12×2.54)/100.0 = 0.30 m
1 m =100.0/(2.54×12.0)= 3.28 ft |
| List of some Units and their conversion from metric to foot-poundal systems : List of some Units and their conversion from metric to foot-poundal systems |
| For Mass : For Mass |
| Prefix for Units : Prefix for Units |
| Some Units in Mechanics : Some Units in Mechanics |
| Some Units in Electricity and Magnetism : Some Units in Electricity and Magnetism |
| Some Abbrevetions : Some Abbrevetions s = second N = newton V = volt
cm = centimeter lb = pound Ω = ohm
m = meter J = joule W = watt
ft = foot Hz = hertz A = Ampere
g = gram mi = mile C = coulomb
kg = kilogram |
| Some Exercises: : Some Exercises: What is 1 inch in terms of a Km ?
1 liter is equal to how many meters ?
1 mile is how many meters ?
What is a light year in terms of meters ?
1 kilogram is equal to how many ounces ?
What is a milli second ?
1 pound is equal to how many grams ?
How many seconds have you lived till today on
earth ?
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| LECTURE-2 : LECTURE-2
MOTION
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| Slide17 : 02CO, p.14 |
| Describing motion : Describing motion Any object moving is said to be in motion.
Motion is signified by change in position of an object
with time
There are different types of motions:
Linear --- moving in a straight line
Circular --- moving in a circle
Helical --- going forward while moving in a circle
Wave and Vibrations ---- ripples in water
and many more…..
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| Helical Motion : Helical Motion |
| How fast do you drive ?? : How fast do you drive ?? Say you are driving back home from school, If
somebody ask you this question what will be your
answer ?
To answer this you need to know how long you have
gone ,that is how far have you travelled and the
time you spent to do so…
Comon !!! Why to do all this we have the speedometer
right ??
True but it actually measures something called speed of
your motion and we will talk about this now.. |
| Speed : Speed Speed is a measure of how fast you are moving.
There are two types of speed
Average Speed
Instantaneous Speed
So what is an average speed ?
It is defined as the total distance you travelled divided
by the total time it took to travel.
Didn’t make any sense right ?? (even if it did I am going
to do this example folks !)
Lets go a bit further with an example |
| Average Speed : Average Speed Let d1, d2, d3, d4 be 4 different distances travelled in time t1 ,t2 ,t3,t4. then the average speed is given by
S = (d1+d2+d3+d4)/(t1+t2+t3+t4) |
| Instantaneous Speed : Instantaneous Speed As the name says this is speed of an object or body at a
particular instant of time.
It is same as average speed for a small time interval.
So if we ask what is the instantaneous speed at say
point A A |
| Slide25 : We will try to figure it out by looking for a small
distance traveled about A for a small time
Hence Instantaneous speed is
Sn|A = Small Distance about A/time spent
The speedometer of a car shows us its instantaneous
speed , not the average.
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| Slide26 : Tom Travels a distance of 10 meters, if the time taken by him to travel this distance is 40 seconds. Find the Average speed in m/s and Km/hr and mile/hr
Let us assume that Tom went from P to L then from L to S. If D1=100 m, T1=25 sec is distance and time he took to go from P to L respectively , D2 =150 m, T2=50 sec is distance and time he took respectively to go from L to S. Find Toms average speed for each part of his journey and the total average speed for the whole journey. |
| Slide28 : Instantaneous Speed can be calculated from a Distance
vs Time graph like the one shown in the earlier slide.
If for example someone ask you what is instantaneous
velocity at Distance = 8 m ?
In the graph draw a line connecting 8 mark on the
vertical axes to the straight line. Now from the point
where it cuts the straight line drop a line to the
horizontal axis below. You can figure out the time.
Divide the distance with this time and you get your
instantaneous speed. |
| Example of Instantaneous Speed : Example of Instantaneous Speed |
| Slide30 : p.18 |
| Slide31 : We have been talking about speed, what if
The moving object is also changing directions ?
We have experienced this--- a car making a turn
It changes direction, while moving
So do we have something to define this kind of
motions ?
Yes we do have ! VELOCITY , this is a quantity which
by definition gives you both speed and the direction
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| Slide32 : Velocity is defined as:
Where ∆ is a greek symbol delta used in physics to
denote change in a quantity. So ∆x is not delta times
x it rather just sigifies a change in quantity x.
Similarly for t. Velocity is a Vector quantity. This are
special type of quantity which have both magnitude
and directions. The bar over x signifies that it is also
a vector quantiy called Displacement.
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| Slide33 : So what is the difference between speed and
Velocity ?
Speed is the measure of how fast a object is going but
Velocity give the direction along which the object is
going with the measure of how fast it is going.
Example: car is going at 60 mph towards east.
The quantity Displacement is different from distance as
Displacement have a sense of direction hidden in it
whereas distance is just the measure of how far you
went. |
| LECTURE-3 : LECTURE-3 We are quite familiar with this term, we always speak of
how fast a car accelerates in compare to other, but
what does it actually means Physically ??
Acceleration is a measure of how quickly you can
change your velocity. It is also a Vector quantity and
have both magnitude and direction.
Another example of acceleration is the motion of a roller
coasters--- next time when you ride it do think about
this.. |
| Slide35 : Acceleration is defined as
When acceleration is along the same direction
as the velocity, speed of the object increases.
If it is along the opposite direction to velocity
speed of the object decreases.
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| Slide36 : Fig. 2-4, p.22 Which one of the two sets of Car accelerates?? |
| Example on Acceleration : Example on Acceleration Consider a car travelling in a highway
speeds up from 35 mph to 65 mph in 10
secs time. What is the acceleration ??
Give your answers in mph/s, km/s2 and
m/s2 |
| Falling bodies : Falling bodies We have been talking till now about bodies
moving along the horizontal direction. What
happens when it falls ?
Does it change speed ,What about the velocity?
Does it Accelerates ??
Let us now address all these questions and see
what happens to a falling body |
| Slide39 : Initially
Speed zero
Velocity zero
Acceleration is zero
In between
Speed increases
Velocity increases
Body accelerates
As it reaches the ground
Speed is zero
Velocity is zero
Acceleration is zero
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| Free Fall : Free Fall A body is said to be falling freely if it falls
through zero air resistance and was not
given any initial velocity
For example dropping a ball through a
pipe from which air has been removed
Under free fall all bodies have the same
acceleration , 9.8 m/s2 or 32 ft/s2 |
| Slide41 : p.24a |
| Slide42 : p.24b |
| Free Fall : Free Fall Who Falls first ?? The elephant or the
feather ?? |
| Slide44 : In free fall objects fall with constant acceleration. Hence
their Speed changes by the same amount for each time
interval.
What if you give an initial velocity to the ball ? For
example you throw a ball upward
It slows , stop and then fall back. The characteristics of
the upward journey is symmetric to the return journey. |
| Slide45 : Say you throw a ball up with a initial
velocity of 29.4 m/s , How long is it going
to take for the ball to stop ? At what
height will it stop ? How far have it fallen
while coming down after 2 secs ? |